is referred to as the influence function of the corresponding
estimator for \(\beta \)  and has mean zero. From the theory of
M-estimation[1]} and semiparametric
theory[2]}, it can be shown the estimator \(\widehat{\beta }\) 
obtained by solving in \(\beta \)  the estimating equation
\(\sum ^n_{i=1}m(Y, A, X; \widehat{\alpha },\beta ) =0,\) 
